As well known, complex fiber reinforced materials comprising such reinforced fibers as carbon fibers, glass fibers and aramid fibers and such matrix resins as epoxy resin are light in weight and superb in mechanical strength and anti-erosion so that they are widely utilized for such products for the general consumers as a fishing rod and a golf rod and structural parts of industrial machinery as well as for the construction of airplanes and space rockets. For manufacturing such products and parts made from such complex fiber reinforced materials as mentioned above and constructing a fixed shape as required, such materials are generally provided in such condition that a matrix resin is impregnated between the component monofilaments of a pre-impregnation sheet made from such reinforced fibers, the improvement on uniform density and thickness of which pre-impregnation sheet is sought after due to the recent expectation for further weight reduction of such products and components of heavy construction.
The large-scale and inexpensive provision of such pre-impregnation sheet uniform in density and smaller in thickness as mentioned above enables not only thinner and lighter shaped products to be mass-produced, but also pre-impregnation sheets whose monofilaments are uni-directionally aligned to be laminated one over another with the direction of the respective sheets horizontally, vertically or diagonally displaced with regard to each other so as to obtain a multiplex pre-impregnation sheet. The production of such an article as being made from such multiplex pre-impregnation sheet as mentioned above could greatly improve rupture strength of such article. Thus, it is highly expected among the respective industrial circles that a reasonable production technology of a thinner spread multi-filaments sheet whose monofilaments are widthwise aligned in parallel and are distributed uniformly in density is established.
In this regard, reasonably producing a pre-impregnation sheet requires that a material cost of reinforced multi-filament bundles to be spread be reduced. Normally, the use of reinforced multi-filament bundle whose monofilaments are less in number with such monofilaments uni-directionally aligned facilitates the production of the pre-impregnation sheet smaller in thickness and whose monofilaments are uniformly distributed in density. However, the reinforced multi-filament bundle whose monofilaments are less in number are expensive in cost so that it is unavoidable that reinforced multi-filament bundle having a number of monofilaments should be used. Thus, it necessitates a method of spreading such reinforced multi-filament bundle having a number of monofilaments to form a thin reinforced multi-filament bundle spread sheet so as to produce a pre-impregnation sheet whose thickness is smaller and whose monofilaments are uniformly distributed in density in a cost-effective manner compared to the prior art.
Conventionally, such methods are known as spreading respective monofilaments by subjecting multi-filament bundles to circular rods, and splitting respective monofilaments widthwise by water stream or high-pressurized air stream and ultrasonically vibrating respective monofilaments bundles so as to split the same. As for some examples of such method by the circular rods, it is disclosed in Japanese Patent Application Laid-open-No. 56-43435 that the multi-filament bundles are passed through and in engagement with a revolving roller that vibrates in the axial direction thereof so as to be spread, and it is disclosed in Japanese After-Grant Patent Application Laid-open No. 3-31823 that the multi-filaments are passed through and in engagement with a plurality of rollers that are disposed in displacement by 30 degrees to 90 degrees to each other so as to be spread. Then, As for some examples of such method by water stream or high-pressurized air stream, it is disclosed in Japanese Patent Application Laid-open No. 52-151362 that the multi-filament bundles are subjected to high-pressurized fluid so as to be spread, and it is disclosed in Japanese Patent Application Laid-open No. 57-77342 that the multi-filament bundles in carriage are subjected to fluid flowing vertically with regard to the moving direction of the former to apply dispersion force by such fluid to the former so as to be spread. Further, as for an example of such ultrasonic method as mentioned above, it is disclosed in Japanese Patent Application Laid-open No. 1-282362 that the multi-filament bundles are put into contact with a circular rod ultrasonically vibrating in the axial direction thereof in a crosswise manner so as to be spread.
However, any one of the above prior arts is intended for spreading multi-filament bundles by applying physical force to the same so as to enforcedly move monofilaments comprising the same widthwise while pulling the multi-filament bundles that tend to recover their converged position. In this reason, it causes the width of spread multi-filament bundle to be made smaller than expected and the monofilaments to be damaged, fluffed and cut after all. In change, in case of such circular rod as mentioned above, enhancing the feeding, speed of the multi-filament bundle causes the friction resistance between the rod and the multi-filament bundle to be larger so as to further increase the number of monofilaments that are cut during operation while in case of such water stream as mentioned above, a larger heating energy is required for drying up the water impregnated with the monofilaments. Accordingly, conventionally, an effective way is not yet to be established to continuously and stably spread the multi-filament bundle with a higher feeding speed.
Under the above circumstances, the subject inventors have proposed in Japanese Patent No. 3049225 entitled ‘Method of producing a spread fibers sheet and an apparatus used in the same’ and in Japanese Patent No. 3064019 entitled ‘Method of producing a spread multi-filaments sheet and an apparatus used in the same’ wherein the multi-filament bundles in a flexibly bent condition are subjected to suction air flowing crosswise with regard to the moving direction of the multi-filament bundles so as to spread the respective multi-filament bundles wider whose monofilaments are uniformly distributed in density. These methods are successful in spreading the respective multi-filament bundles wider whose monofilaments are distributed in density by bending the multi-filament bundles so as to put the monofilaments comprising the same into such condition to facilitate the widthwise movement thereof without enforcement or to put the monofilaments into such condition as facilitating the same to be spread widthwise and by subjecting the monofilaments in such condition to suction air allowing air pass through the respective adjacent monofilaments.
However, such methods as proposed by the subject inventors and mentioned above requires a spreading system in unit at least comprising a front feeder, a suction air cavity, a back feeder and a bending condition measuring sensor. Thus, in order to distribute the monofilaments more uniformly in density and spread the multi-filament bundle more widely, it is required that a series of such spreading systems be disposed in succession so as to gradually proceed with the spreading operation of the same, which results in making the total system becoming much larger-in scale and more complicated in structure while spreading operation being simultaneously performed on a number of multi-filament bundles disposed widthwise, it requires that a set of such spreading systems be arranged side by side, which results in the system as a whole being far larger in scale and by far more complicated in structure.